Why doesn't the Video SEO plugin index all my videos?

Why doesn't the Video SEO plugin index all my videos?

Especially on websites with a large number of videos, the plugin can have problems finding all the videos, due to (a shortage of) memory. You should try re-indexing a number of times, but be sure to leave the 'Force Re-Index' box unchecked. Once the number in the sitemap is static, it has found all videos.